A color photothermographic element containing a mixture of blocked developing agents provides a more robust system for thermal development. In particular, a mixture of at least two blocked developers having different onset temperatures can be used to allow for lower film processing temperatures and/or shorter times of development with respect to the blocked developer having a higher onset temperature, while obtaining improved discrimination with respect to the blocked developer having the lower discrimination. Also, a mixture of at least two blocked developers having different onset temperatures can be used to provide a more robust relative discrimination versus temperature curve.
In conventional color photography, films containing light-sensitive silver halide are employed in hand-held cameras. Upon exposure, the film carries a latent image that is only revealed after suitable processing. These elements have historically been processed by treating the camera-exposed film with at least a developing solution having a developing agent that acts to form an image in cooperation with components in the film. Developing agents commonly used are reducing agents, for example, p-aminophenols or p-phenylenediamines.
Typically, developing agents (also herein referred to as developers) present in developer solutions are brought into reactive association with exposed photographic film elements at the time of processing. Segregation of the developer and the film element has been necessary because the incorporation of developers directly into sensitized photographic elements can lead to desensitization of the silver halide emulsion and undesirable fog. Considerable effort, however, has been directed to producing effective blocked developing agents (also referred to herein as blocked developers) that might be introduced into silver halide emulsion elements without deleterious desensitization or fog effects. Accordingly, blocked developing agents have been sought that would unblock under preselected conditions of development after which such developing agents would be free to participate in image-forming (dye or silver metal forming) reactions.
U.S. Pat. No. 3,342,599 to Reeves discloses the use of Schiff-base developer precursors. Schleigh and Faul, in a Research Disclosure (129 (1975) pp. 27-30), describes the quaternary blocking of color developers and the acetamido blocking of p-phenylenediamines. (All Research Disclosures referenced herein are published by Kenneth Mason Publications, Ltd., Dudley Annex, 12a North Street, Emsworth, Hampshire P010 7DQ, ENGLAND.) Subsequently, U.S. Pat. No. 4,157,915 to Hamaoka et al. and U.S. Pat. No. 4,060,418 to Waxman and Mourning describe the preparation and use of blocked p-phenylenediamines in an image-receiving sheet for color diffusion transfer. In addition to the aforementioned U.S. Pat. No. 4,157,915, blocked developing agents involving xcex2-elimination reactions during unblocking have been disclosed in European Patent Application 393523 and kokais 57076453; 2131253; and 63123046, the latter specifically in the context of photothermographic elements.
All of these approaches have failed in practical product applications because of one or more of the following problems: desensitization of sensitized silver halide; unacceptably slow unblocking kinetics; instability of blocked developer yielding increased fog and/or decreased Dmax after storage, lack of simple methods for releasing the blocked developer, inadequate or poor image formation, and other problems. Especially in the area of photothermographic color films, other potential problems include poor discrimination and poor dye-forming activity.
Recent developments in blocking and switching chemistry have led to blocked developing agents, including p-phenylenediamines, that perform relatively well. In particular, compounds having xe2x80x9cxcex2-ketoesterxe2x80x9d type blocking groups (strictly, xcex2-ketoacyl blocking groups) are described in U.S. Pat. No. 5,019,492. With the advent of the xcex2-ketoester blocking chemistry, it has become possible to incorporate p-phenylenediamine developers in film systems in a form from which they only become active when required for development. The xcex2-ketoacyl blocked developers are released from the film layers in which they are incorporated by an alkaline developing solution containing a dinucleophile, for example hydroxylamine.
It is an object of the invention to obtain improved color photothermographic imaging elements and methods for their development employing incorporated blocked developing agents, also referred to herein as blocked developers. With respect to color photothermographic imaging elements, it is desirable to employ a blocked developer that is stable until development yet can rapidly and easily develop a high quality image once processing has been initiated by heating the element or by applying to the element a processing solution during or after heating, such as a solution of a base or acid or pure water. A completely dry process or an apparently dry process (for example, in which the volume of aqueous solutions is small enough to be applied by a laminate) is most desirable and, in fact, the eliminating the application of all or most solutions and photochemical processing chemicals is one of the main advantages of a dry or apparently dry photothermographic system. The existence of such a process would allow for very rapidly processed films that can be processed simply and efficiently in photoprocessing kiosks. Such kiosks, with increased numbers and accessibility, could ultimately allow for, photofinishing in many new environments that have not previously been attempted. This in turn would lead to increased convenience for the consumer. One of the factors to be considered, with respect to a blocked developer in a color photothermographic element, is the onset temperature of the blocked developer, that is, the temperature at which the compound becomes substantially unblocked or activated, which is generally a measure or indication of the temperature at which the development process will need to be performed. In generally, other factors being equal, the higher the onset temperature, the higher the process temperature. A process at lower temperatures generally has less side reactions and is less expensive to accomplish. There is less potential deformation of the film base which can adversely affect image quality. Also, higher temperatures tend to undesirably decompose components in the photographic element and release volatile vapors.
Another factor to be considered, with respect to a blocked developer in a photothermographic element, is the relative discrimination of the image, generally defined as the difference of between Dmin and Dmax at a given process temperature divided by the Dmin. This parameter describes to ratio of photographic signal to fog level, and is generally desired to be high Since the discrimination of an image, using a blocked developer, will generally vary with process temperature, it is usually desirable to process the film at the temperature of peak discrimination (in the photographic element). It is further desirable that the film have a high peak discrimination. Discrimination of a film can be affected by a number of factors, including photographic emulsion type and finish, the kind and amount of couple, the thermal solvent, and other factors. However, a key factor is the blocked developing agent incorporated in the photothermographic film.
A problem with a blocked developer is that discrimination may be poor if the blocked developer unblocks to quickly or does not unblock quickly enough. It is advantageous to appropriately balance the reactivity of the developing agent, during developing, with the rate of release of the developing agent from the blocked developing agent. If the reactivity of developing agent with the coupling agent (or xe2x80x9ccouplerxe2x80x9d) to form the image dye is too much less than the rate of release of the developing agent, at a particular temperature, then there is the opportunity for side reactions to occur which may decrease the discrimination. (usually by increasing fog) and consequently decrease image quality. On the other hand, if the reactivity of the developing agent with the coupling agent is too much greater than the rate of release of the developing agent, at the temperature of development, then there may not be enough developing agent for image formation to occur which may also decrease discrimination (this time, usually by decreasing Dmax) which again will consequently decrease image quality.
Another problem with blocked developers is that, if the relative discrimination curve (a graph of peak discrimination versus temperature of processing) is too narrow, then the release of the blocked developer in the photographic element as the temperature of the element increases may not be well timed. This may result, for example, in only a small portion of the blocked developer being unblocked as the photographic element is being heated and then, as the element nears the equilibrium temperature, a large amount of blocked developer being unblocked all at once, drowning the coupler with an excess of developing agent, resulting in poor discrimination (high Dmin). It is to be understood that, even though a heater may reach its equilibrium temperature quickly, the photographic element may take some process time to reach its equilibrium or peak temperature, which optionally may be set higher than the temperature of peak discrimination in order to speed the development process.
In general, a broader and flatter relative discrimination curve is desirable. Not only is it more robust relative to variations in process conditions, but it can provide a relatively steady release or unblocking of the developing agent so that the release of the developing agent better matches the reactivity of the developing agent with the coupler and its concentration. This can increase the amount of development occurring at a temperature in the vicinity of peak discrimination for the process. In other words, there is a broader temperature area (element temperature) over which peak discrimination, or near peak discrimination occurs.
Thus, it would be desirable if a higher percentage of peak discrimination for the photothermographic element occurs within over a given temperature range around the peak discrimination temperature, wherein peak discrimination temperature is defined as the temperature at which discrimination peaks when heating the photographic element.
If the relative discrimination curve is narrow, then the photographic element may reach its peak discrimination temperature very quickly without having had time to release the developing agent and then may release the developing agent all at once, which would result, as mentioned above, in the flooding the couplers and poor discrimination. Although one might compensate by heating slower, it is desirable to heat the photographic element quickly to avoid adverse affects of prolonged heating on the photographic element. Thus, it is better to have flatter curve, to provide maximum discrimination for the time period and temperature range of the photothermographic element during the heating process.
In summary of the above, it would be desirable to obtain a photothermographic element, and a method for the thermal development thereof, that is more robust, either by providing a lower processing temperature and/or by providing a flatter relative discrimination curve during thermal processing.
The term xe2x80x9conset temperaturexe2x80x9d or To is defined as the temperature required to produce a maximum density (Dmax) of 0.5, as described in the Examples below. Lower temperatures indicate more active developers which are desirable.
The term xe2x80x9cprocess temperaturexe2x80x9d is defined herein as the maximum temperature present in the photographic element during the development process, which may approximate the maximum temperature of the environment with which the photographic element is directly contacted during the development process, which in turn can approximate the temperature of the heating element (source of heat) during the development process in cases of good heat transfer.
The term xe2x80x9cdiscriminationxe2x80x9d herein generally means the difference between Dmax and Dmin in an imaging layer.
The term xe2x80x9cpeak discriminationxe2x80x9d or Dp is defined, as in the Examples, for the optimum platen temperature, as corresponding to the value of the difference between Dmax and Dmin (Dmaxxe2x88x92Dmin) divided by Dmin.
The term xe2x80x9crelative discrimination curvexe2x80x9d herein means the discrimination as the temperature of the blocked developer varies.
The term xe2x80x9cpeak discrimination temperaturexe2x80x9d herein means the maximum discrimination in the relative discrimination curve.
The term xe2x80x9cExe2x80x9d means herein the exposure in lux-seconds.
The term xe2x80x9ccouplerxe2x80x9d indicates a compound that reacts with oxidized color developing agent to create or modify the hue of a dye chromophore.
In referring to blue, green and red recording dye image-forming layer units, the term xe2x80x9clayer unitxe2x80x9d indicates the hydrophilic colloid layer or layers that contain radiation-sensitive silver halide grains to capture exposing radiation and couplers that react upon development of the grains. The grains and couplers are usually in the same layer, but can be in adjacent layers.
The term xe2x80x9cdye image-forming couplerxe2x80x9d indicates a coupler that reacts with oxidized color developing agent to produce a dye image.
Research Disclosure is published by Kenneth Mason Publications, Ltd., Dudley House, 12 North St., Emsworth, Hampshire PO10 7DQ, England.
The term xe2x80x9cone-time-use cameraxe2x80x9d or xe2x80x9cOTUCxe2x80x9d is used to indicate a camera supplied to the user preloaded with a light sensitive silver halide photographic element and having a lens and shutter. The terms xe2x80x9csingle-use camera,xe2x80x9d xe2x80x9cfilm-with-lens unit,xe2x80x9d xe2x80x9cdisposable cameraxe2x80x9d and the like are also employed in the art for cameras that are intended for one use, after which they are recycled, subsequent to removal of the film for development.
This invention relates to a photothermographic color element containing a mixture of at least two different blocked developers in the same emulsion layer, which blocked developers have different onset temperatures. By different blocked developers is meant two blocked developing agents having (1) the same developing agent upon unblocking, but having different blocking/timing groups, (2) the same blocking and/or timing groups but different developing agents when unblocked, and/or (3) both different developing agents upon complete unblocking and different blocking and/or timing groups.
The term blocking/timing group is meant the portion of the blocked developer other than the developing agent that reacts with a coupler. The blocking/timing group, therefore, separates from the developing agent, even if in stages, over time.
In one embodiment of the invention, mixtures of blocked developers have been found that provide lower processing temperatures and/or shorter times of development compared to the blocked developer alone having the higher onset temperature, and at the same time, improved discrimination compared to the blocked developer alone having the lower onset temperature. In some cases, higher peak discrimination than obtainable with either of the blocked developers alone at the given process temperature is obtainable.
In another embodiment of the invention, mixtures of blocked developers have been found that provide a lower slope f the relative discrimination versus temperature curve, thereby providing a flatter and more robust relative discrimination curve compared to either blocked developer alone.
Preferably, when the developer mixture is used in a dry physical development system, the developer is thermally activated at temperatures between about 80 and 180xc2x0 C., preferably 100 to 170xc2x0 C. When the developer is used in an apparently dry chemical development system, however, the developer mixture is preferably thermally activated at temperatures between about 60 and 120xc2x0 C., preferable 65 to 100xc2x0 C., in the presence of added acid, base or water.
In particular, the present invention is directed to a color photothermographic color element comprising at least three light-sensitive units that have their individual sensitivities in different wavelength regions comprising a silver halide imaging layer having associated therewith a mixture of at least two locked developing agents comprising a Blocked Developer A and blocked Developer B independently represented by Structure I:
xe2x80x83DEV-(LINK, 1)l-(TIME)m-(LINK2)n-Mxe2x80x83xe2x80x83I
wherein,
DEV is a silver-halide color developing agent;
LINK 1 and LINK 2 are linking groups;
TIME is a timing group;
l is 0 or 1;
m is 0, 1, or2;
n is 0 or 1;
l+n is 1 or 2;
M is a blocking group or M is:
-Mxe2x80x2-(LINK 2)n-(TIME)m-(LINK 1)l-DEV
xe2x80x83wherein Mxe2x80x2 is a blocking group that also contains another blocked developer, which may be the same or a different developing agents; and
wherein the onset temperature of Blocked Developer A is less than the onset temperature of Blocked Developer B, the onset temperature of Blocked Developer A is in the range of 110xc2x0 C. to 160xc2x0C., preferably 110 to 150xc2x0 C., and the onset temperature of Blocked Developer B is in the range of 130 to 170xc2x0 C., preferably 140 to 160xc2x0 C., and the difference in the onset temperatures of the two Blocked Developers is 5 to 50xc2x0 C., preferably 8 to 40xc2x0 C., more preferably 10 to 30xc2x0 C.
In a preferred embodiment of the invention, the peak discrimination of the mixture of Blocked Developer A and Blocked Developer B will be higher than the discrimination of Blocked Developer B. In a particularly preferred embodiment, the peak discrimination of the mixture is higher than the peak discrimination of both Blocked Developer A and Blocked Developer B.
The invention additionally relates to a method of image formation having the steps of: thermally developing an imagewise exposed photographic element having a mixture of blocked developers as described above that decomposes to release corresponding developing agents on thermal activation to form a developed image. Preferably, following development, the developed image is then scanned to form a first electronic-image representation (or xe2x80x9celectronic recordxe2x80x9d) from said developed image, the first electronic record is digitized to form a digital image, and the digital image is modified to form a second electronic-image representation, which can be stored, transmitted, printed or displayed.
The invention further relates to a one-time use camera having a light sensitive photographic element comprising a support and a mixture of blocked developers as described above that releases a mixture of developing agents or differentially releases the same developing agents (in the same or different imaging layers) on thermal activation. The invention further relates to a method of image formation having the steps of imagewise exposing such a light sensitive photographic element on thermal activation in a one-time-use camera having a heater and thermally processing the exposed element in the camera.
In a preferred embodiment of the invention, LINK 1 and LINK 2 are of structure II: 
wherein
X represents carbon or sulfur;
Y represents oxygen, sulfur or Nxe2x80x94R1, where R1 is substituted or unsubstituted alkyl or substituted or unsubstituted aryl;
p is 1 or 2;
Z represents carbon, oxygen or sulfur;
r is 0 or 1; with the proviso that when X is carbon, both p and r are 1, when X is sulfur, Y is oxygen, p is 2and r is 0;
# denotes the bond to PUG (for LINK 1) or TIME (for LINK 2):
$ denotes the bond to TIME (for LINK 1) or T(t) substituted carbon (for LINK 2).